package com.hdw.common.util.security;

import java.io.UnsupportedEncodingException;

/**
 * Hex encoder and decoder. The charset used for certain operation can be set,
 * the default is set in
 *
 * @author TuMinglong
 * @version $Id: Hex.java, v 0.1 2014年3月25日 上午9:39:07 ShenHuaJie Exp $
 */
public class Hex {

    /***
     * Default charset name is UTF_8
     */
    public static final String DEFAULT_CHARSET_NAME = "UTF-8";

    /***
     * Used to build output as Hex
     */
    private static final char[] DIGITS_LOWER = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd',
            'e', 'f'};

    /***
     * Used to build output as Hex
     */
    private static final char[] DIGITS_UPPER = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D',
            'E', 'F'};

    /***
     * Converts an array of characters representing hexadecimal values into an
     * array of bytes of those same values. The returned array will be half the
     * length of the passed array, as it takes two characters to represent any
     * given byte. An exception is thrown if the passed char array has an odd
     * number of elements.
     *
     * @param data An array of characters containing hexadecimal digits
     * @return A byte array containing binary data decoded from the supplied
     *         char array.
     * @throws Exception Thrown if an odd number or illegal of characters is
     *             supplied
     */
    public static byte[] decodeHex(char[] data) throws Exception {

        int len = data.length;

        if ((len & 0x01) != 0) {
            throw new Exception("Odd number of characters.");
        }

        byte[] out = new byte[len >> 1];

        // two characters form the hex value.
        for (int i = 0, j = 0; j < len; i++) {
            int f = toDigit(data[j], j) << 4;
            j++;
            f = f | toDigit(data[j], j);
            j++;
            out[i] = (byte) (f & 0xFF);
        }

        return out;
    }

    /***
     * Converts an array of bytes into an array of characters representing the
     * hexadecimal values of each byte in order. The returned array will be
     * double the length of the passed array, as it takes two characters to
     * represent any given byte.
     *
     * @param data a byte[] to convert to Hex characters
     * @return A char[] containing hexadecimal characters
     */
    public static char[] encodeHex(byte[] data) {
        return encodeHex(data, true);
    }

    /***
     * Converts an array of bytes into an array of characters representing the
     * hexadecimal values of each byte in order. The returned array will be
     * double the length of the passed array, as it takes two characters to
     * represent any given byte.
     *
     * @param data a byte[] to convert to Hex characters
     * @param toLowerCase <code>true</code> converts to lowercase,
     *            <code>false</code> to uppercase
     * @return A char[] containing hexadecimal characters
     * @since 1.4
     */
    public static char[] encodeHex(byte[] data, boolean toLowerCase) {
        return encodeHex(data, toLowerCase ? DIGITS_LOWER : DIGITS_UPPER);
    }

    /***
     * Converts an array of bytes into an array of characters representing the
     * hexadecimal values of each byte in order. The returned array will be
     * double the length of the passed array, as it takes two characters to
     * represent any given byte.
     *
     * @param data a byte[] to convert to Hex characters
     * @param toDigits the output alphabet
     * @return A char[] containing hexadecimal characters
     * @since 1.4
     */
    protected static char[] encodeHex(byte[] data, char[] toDigits) {
        int l = data.length;
        char[] out = new char[l << 1];
        // two characters form the hex value.
        for (int i = 0, j = 0; i < l; i++) {
            out[j++] = toDigits[(0xF0 & data[i]) >>> 4];
            out[j++] = toDigits[0x0F & data[i]];
        }
        return out;
    }

    /***
     * Converts an array of bytes into a String representing the hexadecimal
     * values of each byte in order. The returned String will be double the
     * length of the passed array, as it takes two characters to represent any
     * given byte.
     *
     * @param data a byte[] to convert to Hex characters
     * @return A String containing hexadecimal characters
     * @since 1.4
     */
    public static String encodeHexString(byte[] data) {
        return new String(encodeHex(data));
    }

    /***
     * Converts a hexadecimal character to an integer.
     *
     * @param ch A character to convert to an integer digit
     * @param index The index of the character in the source
     * @return An integer
     * @throws Exception Thrown if ch is an illegal hex character
     */
    protected static int toDigit(char ch, int index) throws Exception {
        int digit = Character.digit(ch, 16);
        if (digit == -1) {
            throw new Exception("Illegal hexadecimal charcter " + ch + " at index " + index);
        }
        return digit;
    }

    private static String charsetName = DEFAULT_CHARSET_NAME;

    /***
     * Creates a new codec with the default charset name
     * {@link #DEFAULT_CHARSET_NAME}
     */
    public Hex() {
    }

    /***
     * Creates a new codec with the given charset name.
     *
     * @param csName the charset name.
     * @since 1.4
     */
    public Hex(String csName) {
        charsetName = csName;
    }

    /***
     * Converts an array of character bytes representing hexadecimal values into
     * an array of bytes of those same values. The returned array will be half
     * the length of the passed array, as it takes two characters to represent
     * any given byte. An exception is thrown if the passed char array has an
     * odd number of elements.
     *
     * @param array An array of character bytes containing hexadecimal digits
     * @return A byte array containing binary data decoded from the supplied
     *         byte array (representing characters).
     * @throws Exception Thrown if an odd number of characters is supplied to
     *             this function
     * @see #decodeHex(char[])
     */
    public byte[] decode(byte[] array) throws Exception {
        try {
            return decodeHex(new String(array, getCharsetName()).toCharArray());
        } catch (Exception e) {
            throw new Exception(e.getMessage(), e);
        }
    }

    /***
     * Converts a String or an array of character bytes representing hexadecimal
     * values into an array of bytes of those same values. The returned array
     * will be half the length of the passed String or array, as it takes two
     * characters to represent any given byte. An exception is thrown if the
     * passed char array has an odd number of elements.
     *
     * @param object A String or, an array of character bytes containing
     *            hexadecimal digits
     * @return A byte array containing binary data decoded from the supplied
     *         byte array (representing characters).
     * @throws Exception Thrown if an odd number of characters is supplied to
     *             this function or the object is not a String or char[]
     * @see #decodeHex(char[])
     */
    public Object decode(Object object) throws Exception {
        try {
            char[] charArray = object instanceof String ? ((String) object).toCharArray() : (char[]) object;
            return decodeHex(charArray);
        } catch (ClassCastException e) {
            throw new Exception(e.getMessage(), e);
        }
    }

    /***
     * Converts an array of bytes into an array of bytes for the characters
     * representing the hexadecimal values of each byte in order. The returned
     * array will be double the length of the passed array, as it takes two
     * characters to represent any given byte.
     * <p>
     * The conversion from hexadecimal characters to the returned bytes is
     * performed with the charset named by {@link #getCharsetName()}.
     * </p>
     *
     * @param array a byte[] to convert to Hex characters
     * @return A byte[] containing the bytes of the hexadecimal characters
     * @throws IllegalStateException if the charsetName is invalid. This API
     *             throws {@link IllegalStateException} instead of
     *             {@link Exception} for backward compatibility.
     * @see #encodeHex(byte[])
     */
    public static byte[] encode(byte[] array) throws UnsupportedEncodingException {
        String string = encodeHexString(array);
        if (string == null) {
            return null;
        }
        return string.getBytes(charsetName);
    }

    /***
     * Converts a String or an array of bytes into an array of characters
     * representing the hexadecimal values of each byte in order. The returned
     * array will be double the length of the passed String or array, as it
     * takes two characters to represent any given byte.
     * <p>
     * The conversion from hexadecimal characters to bytes to be encoded to
     * performed with the charset named by {@link #getCharsetName()}.
     * </p>
     *
     * @param object a String, or byte[] to convert to Hex characters
     * @return A char[] containing hexadecimal characters
     * @throws Exception Thrown if the given object is not a String or byte[]
     * @see #encodeHex(byte[])
     */
    public Object encode(Object object) throws Exception {
        try {
            byte[] byteArray = object instanceof String ? ((String) object).getBytes(getCharsetName())
                    : (byte[]) object;
            return encodeHex(byteArray);
        } catch (ClassCastException e) {
            throw new Exception(e.getMessage(), e);
        } catch (Exception e) {
            throw new Exception(e.getMessage(), e);
        }
    }

    /***
     * Gets the charset name.
     *
     * @return the charset name.
     * @since 1.4
     */
    public String getCharsetName() {
        return charsetName;
    }

    /***
     * Returns a string representation of the object, which includes the charset
     * name.
     *
     * @return a string representation of the object.
     */
    public String toString() {
        return super.toString() + "[charsetName=" + charsetName + "]";
    }
}
